SLSTR A Spot

New Processing Baselines for SLSTR Level 1 & 2 SST

 

SLSTR A Spot
SLSTR A Spot

New Processing Baselines for Sentinel-3 SLSTR Level 1 and Level 2 SST are planned to be released on 18 January 2022.

Last Updated

13 January 2022

Published on

16 December 2021

The new Processing Baselines (PB) are SL__L1_.004.04 for Sentinel-3 SLSTR Level 1 (L1) RBT products and SL__SST.003.06 for Sentinel-3 SLSTR Level 2 (L2) SST products.

The update includes a new version of the SLSTR L1 RBT Instrument Processing Facility (IPF), v06.19, and a new version of the SLSTR L2 SST IPF, v06.20. The baseline collection numbers of the SLSTR L1 RBT products (004) and SLSTR L2 SST products (003) are unchanged.

The main reasons for the update are the transfer of the Bayesian cloud mask from the L1 IPF to the L2 IPF and the addition of the PB identifier to the Manifest and netCDF files within the SAFE format output products.

At the same time a new version of Product Unit Generation (PUG), v03.43 will be released. This update is released to all IPFs using the PUG (SL1/SL2 SST, OL1/OL2 OC) but is applicable to SLSTR L1.

Changes introduced in new SLSTR L1 PB SL__L1_.004.04

  • Removal of Probabilistic and Bayesian cloud masks from L1 processing.
  • Addition of PB identifier to Manifest and netCDF files.
  • Revised VISCAL processing.
  • Revised saturation flagging for all channels.
  • Corrected errors in meteorological attributes.
  • Corrected pixel statistics in Manifest file for F1 grid.

Changes introduced in new SLSTR L2 SST PB SL__SST.003.06

  • Transfer of Bayesian cloud mask processing from L1 to L2 SST and removal of Probabilistic mask over land surfaces
  • Addition of PB identifier to Manifest and netCDF files.

Changes introduced in PUG version 3.43 applicable to SLSTR L1

PUG: Improved PDU SLSTR L1 manifest flagging during manoeuvres.

Further details of changes and impacts

The main change in these updates is the removal of the Bayesian/Probabilistic cloud mask processing from SLSTR L1 and transfer of Bayesian cloud mask processing to SLSTR L2 SST. As a result the probability and Bayesian cloud flags within the flags annotation datasets in the SLSTR L1 RBT products are no longer calculated and only water pixels in SLSTR L2 SST are processed with Bayesian cloud mask.

The SLSTR L1 and SLSTR L2 SST products now contain a PB identifier within the Manifest file and within global attributes of all netCDF files in the SAFE format output products. The PB identifier uniquely identifies individual products (e.g. SL__L1_ or SL__SST for SLSTR L1 and SLSTR L2 SST, respectively), as well as their major (baseline collection) and minor (changes in the IPF version and/or auxiliary data file) version numbers (Figure 1).

Example of addition of SLSTR L2 SST PB identifier to Manifest file (upper) and NetCDF files (lower)
Figure 1: Example of addition of SLSTR L2 SST PB identifier to Manifest file (upper) and netCDF files (lower).

Two updates have been made to the VISCAL processing of the on-board calibration for channels S1 to S6. First, a revised algorithm has been implemented to improve noise estimates from the VISCAL signal. The current operational noise values are overestimated and the new values are more in line with pre-launch estimates. In addition, a revision has been made to the VISCAL calculation to account for missing scans in the instrument Level 0 data, should they arise.

The check for channel saturation during calibration has been reorganised within the IPF processing steps to ensure this occurs before the non-linearity corrections are applied. The non-linearity correction could increase the number of detector counts, so falsely flagged pixels are now correctly identified as being within the valid dynamic range of the channel. Users will see an increase in valid pixels for high scene radiances in channels S1, S2, S3 and S8 on SLSTR-A and in channels S1, S2 and S3 on SLSTR-B. An example is shown in the figure below (Figure 2).

Example of S3A SLSTR L1 product where saturated pixels (left) are no longer present in the new processing version (right)
Figure 2: Example of S3A SLSTR L1 product where saturated pixels (left) are no longer present in the new processing version (right).

Several changes have been made to the variable attributes for the meteorological annotations provided in the met_tx.nc files.

A revised algorithm for calculating the pixel-level statistics reported in the Manifest file for the F1 grid has been included that correctly accounts for any data gaps in the input L0 data.

There is no impact on SST data quality as a result of these updates. Sea surface temperature users should only use quality level 5 data for the best quality sea surface temperature observations, and should ensure they always apply the SSES to minimise the impact of the change.

Similarly, these changes have no impacts on the current L2 NRT Aerosols and NRT Fires. Although a higher number of high scene radiances are now read by these processors, they are all properly screened thanks to their associated cloud mask and glint detection modules, leading to zero change in the L2 product outputs. Contrary to the L2 SST, the PB identifier of L2 NRT Aerosols and Fires are not yet visible and will be added into the respective manifest files during spring 2022. Specific announcements will be sent in due time.

The new PUG version is now using exact start and stop manoeuvre and thrust times to flag only PDUs (Product Dissemination Units - 3 min granules) impacted by manoeuvre or thrust.

Further details of all the updates will be provided in the updated Product Notices accompanying the release and which will be made available from http://slstr.eumetsat.int in January 2022.

For more information, contact our User Service Helpdesk.